Synthesis Of Copper,Zinc And Iron Complexes Derived From Aminopyridine And Their Catalysis For Lactide Polymerization

In recent years,poly(lactic acid)(PLA),as an excellent biodegradable environmental protection material,has attracted the attention of researchers,and it has also become the focus of green and sustainable development.Polylactic acid(PLA)is widely used in the fields of medical treatment,textile industry,agriculture,cosmetics and chemical plastics because of its biodegradability and good biocompatibility.Up to now,stannous octanoate catalyst is the only catalyst that can be widely used in industry to catalyze the polymerization of lactide to poly(lactic acid)(PLA).However,the molecular weight distribution of PLA synthesized by this method is wide and there are many side reactions.Therefore,it is urgent to develop new catalysts with good catalytic performance.In this paper,a series of new air-stable copper,iron and zinc complexes were designed and synthesized,and their catalytic properties of racemic lactide were further studied.This paper is divided into the following four parts:1.The preparation methods,structural characteristics,thermal stability and catalytic effect of salen-Cu complexes for rac-LA were introduced.Ten salenligands were synthesized from 2-aminomethylpyridine,2-(2-aminoethyl)pyridine and salicylaldehyde derivatives.These ligands can react with CuX2(X=Cl,OAc,OTf)to form corresponding Cu(Ⅱ)metal complexes with air stability.The structures of 10 ligands and 8 Cu(Ⅱ)metal complexes were identified by IR,TGA and X-ray single crystal diffraction.These salen-Cu complexes can be used as catalysts for the bulk ring-opening polymerization of racemic lactide with moderate catalytic effect.at the same time,the prepared poly(lactide)has low molecular weight and wide molecular weight distribution.2.The preparation methods,structural characteristics,thermal stability and catalytic effect of salen-Zn complexes for rac-LA were introduced.Two Clsubstituted ligands with electron absorbing effect were synthesized from 2-(2-aminoethyl)pyridine and salicylaldehyde derivatives.These ligands can complex with ZnCl2 and Zn(OAc)2 in air to form corresponding Zn(Ⅱ)metal complexes with air stability.The structures and stability of all the prepared ligands and zinc metal complexes were characterized by NMR,IR,TGA and X-ray single crystal diffraction.These salen-Zn complexes can be used as catalysts for bulk ring-opening polymerization of racemic lactide and show moderate catalytic effect.3.The synthesis,structure,thermal stability and catalytic performance of iron complexes for rac-LA were introduced.Two Cl-substituted ligands with electron withdrawing effect and one ligand with electron donor tBu-substituent were synthesized from 2-aminomethylpyridine,2-(2-aminoethyl)pyridine and salicylaldehyde derivatives.These ligands react with FeCl3 to form corresponding Fe(Ⅲ)metal complexes with air stability.The structures of three ligands and three iron complexes were identified by IR,TGA and X-ray single crystal diffraction.Finally,these iron complexes were used as catalysts for the polymerization of racemic lactide and showed moderate catalytic effect.